Sterile mosquitoes vs mosquito spraying

How long does mosquito spray last?

Weeks at most, and less after rain. Then the clock resets and the next visit is booked.

A short window. Texas A&M AgriLife Extension rates yard sprays such as bifenthrin and lambda-cyhalothrin as lasting "days to weeks," and says residual sprays can suppress mosquitoes for up to a month.¹ That's the upper end, in good conditions.

Rain, sprinklers and sun wear it down. AgriLife notes that an insecticide's residual life depends on temperature, sunlight and exposure to water.¹ In one study of bifenthrin-treated shrubs, repeated heavy rain cut the spray's effect on mosquitoes within one week of treatment, and leaves in full sun lost effectiveness faster than leaves in shade.⁸ After a wet week, the protection you paid for may already be gone.

The reapplication treadmill. Because the residue fades, spraying is sold as a schedule, not a fix. Professional programs in Dallas-Fort Worth usually retreat about every three weeks, all season.² Miss a visit, or get a stormy stretch, and mosquitoes are back.

It can't reach where mosquitoes breed. A spray protects the leaves it lands on. Eggs and larvae in clogged gutters, tree holes, plant saucers and storm drains keep developing.¹ In a study in Brazil, researchers found storm drains serve as breeding and resting sites for both Asian tiger and yellow fever mosquitoes, and that control campaigns usually overlook them.⁹ The yard next door isn't treated at all.

Nothing to wear off. There's no residue for rain to wash away or sun to break down. Each release adds fresh males, and they find wild females on their own, including in spots that are hard to treat. Their eggs don't hatch, so each generation is smaller than the last. Sterile males work on the next generation, so the effect keeps building.

How barrier spraying works

A technician treats the places mosquitoes rest between bites. Anything that lands there picks up the insecticide.

Adult mosquitoes spend the hot part of the day in shade: under leaves, in tall grass, in shrubs and along the sides of the house. A barrier treatment, usually applied with a backpack mist blower, coats those surfaces with a long-lasting insecticide. Common active ingredients are pyrethroids such as bifenthrin, cyfluthrin, deltamethrin and lambda-cyhalothrin.¹

It does work on the adults it reaches. In a University of Kentucky study of suburban yards, two pyrethroid barrier sprays cut Asian tiger mosquito landing rates by about 85% to 90% four weeks after treatment. The same study found no drop in the night biters.³

What a spray can't touch is the next generation. Eggs and larvae in gutters, plant saucers, tree holes and drains keep developing, so new adults keep emerging. Asian tiger and yellow fever mosquitoes usually live within 200 to 300 yards of where they hatched, which means the source is often your yard or the one next door.¹

How sterile males work

Biological control that's precisely targeted: it affects only the two mosquito species we release, so people, pets, bees and butterflies are untouched.

A spray waits on the leaves for mosquitoes to land. Sterile males go looking for wild females, including where sprays and traps can't reach, and the eggs from those matings don't hatch.

More on the process: How it works

Side by side

A quick read for anyone weighing a treatment contract against a season of sterile males.

When spraying is the right choice

Every tool has a job. Here's where a spray earns its place.

An event in a hurry, before releases start. If the wedding or graduation party is next weekend and the yard is full of mosquitoes today, a spray works sooner than we can. Sterile males work on the next generation, so the effect keeps building.

Night biters. Our releases target Aedes only. If the mosquitoes bothering you come out after dark, they're likely a different species, and sterile males won't reduce them. Removing standing water, larvicides and repellent are the tools for that. Note that the Kentucky study above didn't find barrier sprays reduced the night biters either.³

If you do spray, AgriLife's advice is to spray in the evening and avoid blooming plants, to limit harm to bees and other beneficial insects.¹

Is your spray still working?

The CDC says mosquito populations can develop resistance when insecticides are used repeatedly over time, until a product only partly works, "even when used as directed."⁷ That's one reason the same spray can seem weaker each year. Sterile males sidestep the problem: there is no insecticide to resist.

The full side-by-side of every option is on Compare all options. Two close cousins of barrier spraying: fogging and misting systems.

Using them together

Switching is one step. A residual spray kills any mosquito that rests on treated leaves, including the males we release, so if you want one last spray, do it at least one week before your first release. Once releases start, stop spraying.

Whatever you choose, tip out standing water after rain: buckets, plant saucers, toys and clogged gutters. It helps every program, ours included. Our page on larvicides and dunks covers water you can't dump.